The present invention relates to cellulose particles and to methods for producing such particles. The present invention further deals with applications of the cellulose particles.
Due to various measures such as circuit concentration, increased use of de-inking pulps and high-yield pulps such as wood pulp and TMP (thermomechanic pulp), and neutral processing, there has been an increase in the load of interfering substances (trash) in water circuits of the paper industry.
Interfering substances were first defined as all substances that reduce the efficacy of cationic retention aids in the paper stock, i.e. those substances added in order to improve the retention of the fiber/filler mixture. Recently this definition has been more precisely stated as interfering substances are generally, dissolved or colloidally dissolved anionic oligomers or polymers and nonionic hydrocolloids.
These interfering substances have different effects. They impair the action of retention aids, dry- and wet-strength agents, i.e. substances increasing the strength of the paper, and furthermore lead to deposits in the paper machine circuit, forming drainage disturbances and a loss of paper strength, whiteness and opacity.
In order to eliminate the adverse effects of these interfering substances on papermaking one uses alum, polyaluminum chloride, low-and high-molecular fixers, cationic starch and inorganic adsorbents. All these substances become attached to the anionic trash with the aid of electrostatic interactions and form complexes therewith. Through binding of these complexes to the fibers or through filtration, these aggregates are removed from the paper machine system.
However, all these products have their own disadvantages. For example aluminum salts can only be used to a limited extent in neutral processing, which is gaining importance due to the increasing use of calcium carbonate as a filler, since they are not cationically charged and thus not very effective in this pH range.
The use of highly charged, cationic polyelectrolytes in turn involves the problem of exact metering. Otherwise an overcationization of the paper machine circuit and thus cationic dispersion can occur. This means that there can be poor fine-substance retention and reduced sizing.
The present invention addresses the foregoing noted objectives and provides, in a first aspect, a cellulose particle comprising cationic groups wherein at least 10% of the cationic groups are present in the interior of the particle.
In yet another aspect, the present invention provides cellulose particles having cationic groups that are distributed across the entire cross section of the particles. The concentration of the cationic groups is constant or preferably, increases from the exterior to the interior of the particles. The particles include at least one cationic group per 100 anhydroglucose units of cellulose.
In yet another aspect, the present invention provides an aqueous system comprising water, a water soluble polymer, and cellulose particles having cationic groups, wherein the cationic groups are present in the interior of the particles.